Joule heated melters have traditionally been used for the production of glass-based products. Graphite electrode arc melters have traditionally been used for the reduction of ores to metals and for the production of value added products from a controlled and well defined input feed steam. Arc melters have also been used for the production of a value added mineral wool product from a well characterized and controlled input feedstock. Plasma arc torch melters have traditionally been used for the production of higher value precious metals such as titanium. The various types of melters commonly used in industry can be classified as low temperature (900.degree. C.-1,200.degree. C.) medium temperature (1,200.degree. C.-1,500.degree. C.) and high temperature (1,500.degree. C.-2,000.degree. C.), with their use defined by the product desired and process required. The joule heated melters commonly used for the production of glass (including borosilicate glass for high level radioactive waste) fall into the low temperature range. Medium temperature melters are required for the production of higher temperature glasses such as aluminosilicate glasses and glass ceramics.
High temperature melters are required for the reduction of ores to metals such as iron ore to iron and for the production of a basalt-like glass ceramic product without the addition of fluxing agents to lower the viscosity. Arc melters use heat generated when an electric arc passes through a gas. The gas is ionized and forms a very high temperature plasma. The plasma temperatures can exceed many thousands of degrees centigrade. The high temperatures enable rapid and intense heating of process materials, making this technology ideal for high temperature metals processing.
Current research and development by government and industry is being pursued for the purpose of applying arc melter technology to the treatment of hazardous and/or radioactive wastes. The application of traditional melter technology and equipment to the safe, efficient and economical treatment of heterogeneous hazardous and/or radioactive waste involves the expansion of the allowable makeup of the input feed stream, the expansion of the flexibility of process operation, and the tightening of specifications for the output products and offgases.
There have been a number of testing or development programs to apply electric arc melter technology to the treatment of radioactive wastes, mixed wastes, municipal wastes, and hazardous wastes. In an arc melter, waste materials are heated to (a) volatilize, pyrolyze, and destroy organics, and (b) melt inorganic materials into molten slag or metal phases. By controlling reaction stoichiometry, mixing, and other operating parameters, the process can be used to chemically oxidize or reduce waste components, or react waste components to form new products.
Leam In U.S. Pat. No. 4,421,037 discusses a waste treatment furnace.
Rackley, et al. In U.S. Pat. No. 5,052,312 discusses a cyclone furnace for hazardous waste incineration and ash vitrification.
Alvi, et al. In U.S. Pat. No. 5,541,386 discusses the plasma arc decomposition of hazardous waste into vitrified solids and non-hazardous gasses.